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Abstract:

Provided is a sealed battery that can offer excellent battery performances
by having its electrode terminal and a current collector securely welded
to each other, and its manufacturing method. The sealed battery is formed
by hermetically sealing a casing storing an electrode assembly and the
current collector, wherein: the electrode assembly formed by layering
positive and negative electrode plates with a separator sandwiched
therebetween is electrically connected to the current collector; and a
shaft portion of the electrode terminal penetrates through the current
collector. A part of the electrode terminal projecting out from a
pass-through of the current collector is a (conical) frustum-shaped
portion whose bottom base is in contact with the current collector. The
frustum-shaped portion is pressed against the current collector, and the
frustum-shaped portion and the current collector are welded together in
at least one area on a perimeter of the bottom base of the frustum-shaped
portion.

Claims:

1. A sealed battery formed by hermetically sealing an external casing
storing therein an electrode assembly that is (i) electrically connected
to a current collector and (ii) formed by layering a positive electrode
plate and a negative electrode plate with a separator sandwiched
therebetween, the current collector being welded together with an
electrode terminal, whereinthe electrode terminal is composed of (i) a
shaft portion, (ii) a terminal portion provided in a first end of the
shaft portion and (iii) a frustum-shaped portion provided in a second end
of the shaft portion,the shaft portion penetrates through the current
collector such that the frustum-shaped portion projects out from the
current collector,the frustum-shaped portion has been pressed against the
current collector such that a bottom base of the frustum-shaped portion
comes into contact with the current collector, andthe bottom base of the
frustum-shaped portion and the current collector have been welded
together in at least one area on a perimeter of the bottom base of the
frustum-shaped portion.

2. The sealed battery of claim 1, whereinthe frustum-shaped portion is an
expanded portion formed by diametrically expanding a shaft-like apical
portion that (i) is provided in the second end of the shaft portion and
(ii) has an opening that connects to an external space in the penetration
direction, andthe shaft-like apical portion is diametrically expanded by
flaring the opening with a jig inserted thereinto.

4. The sealed battery of claim 1, whereinthe frustum-shaped portion has a
shape of a conical frustum.

5. A manufacturing method for a sealed battery, comprising:a first step of
(i) causing a terminal element, which is composed of a shaft portion and
an apical portion provided in a first end of the shaft portion, to
penetrate through a current collector such that the apical portion
projects out from the current collector, (ii) shaping the apical portion
into a plate-like portion by expanding the apical portion diametrically
and (iii) pressing the plate-like portion against the current collector;a
second step of shaping the plate-like portion into a frustum-shaped
portion whose bottom base is facing the current collector; anda third
step of welding the bottom base of the frustum-shaped portion and the
current collector together in at least one area on a perimeter of the
bottom base of the frustum-shaped portion, such that the bottom base of
the frustum-shaped portion is in contact with the current collector.

6. The manufacturing method of claim 5, wherein in the second step, the
plate-like portion is shaped into the frustum-shaped portion by deforming
the plate-like portion using a pressing die.

7. A manufacturing method for a sealed battery, comprising:a first step of
causing a terminal element, which is composed of a shaft portion and an
apical portion provided in a first end of the shaft portion, to penetrate
through a current collector such that the apical portion projects out
from the current collector, wherein the apical portion has a cup-shaped
opening that connects to an external space in the penetration direction;a
second step of forming a frustum-shaped portion whose bottom base is
facing the current collector by (i) diametrically expanding the apical
portion by flaring the cup-shaped opening with a jig inserted thereinto
and (ii) pressing the frustum-shaped portion against the current
collector; anda third step of welding the frustum-shaped portion and the
current collector in at least one area on a perimeter of the bottom base
of the frustum-shaped portion.

Description:

BACKGROUND OF THE INVENTION

[0001](1) Field of the Invention

[0002]The present invention relates to a sealed battery and a
manufacturing method for the same, and in particular to technology for
properly welding an electrode terminal to a current collector in the
manufacturing process.

[0003](2) Description of the Related Art

[0004]In recent years, mobile electronic devices, such as mobile phones
and personal digital assistants (PDAs), have been disseminated rapidly.

[0005]In these electronic devices, sealed batteries, such as nickel-metal
hydride (Ni-MH) batteries and lithium-ion batteries, are frequently used
as high-energy density power sources.

[0006]Generally, a sealed battery is formed by storing an electrode
assembly and electrolyte into a rectangular external casing with a closed
bottom, then sealing an opening in the external casing with a sealing
plate (note, the shape of the external casing is not limited to a
rectangular shape). The electrode assembly is formed, for example, by
rolling a negative electrode plate and a positive electrode plate that
have been layered with a belt-like separator sandwiched therebetween. The
negative electrode plate is connected via a lead tab to a current
collector. The current collector is connected to an electrode terminal
(negative electrode terminal) provided in a sealing assembly. The
positive electrode plate is connected via another lead tab to the
external casing that also functions as a positive electrode terminal.

[0007]A manufacturing process for a sealed battery is described in, for
example, Japanese Laid-Open Patent Applications No. 2003-272604 and No.
2001-291506. The following is one example of methods described in these
documents. To begin with, the electrode assembly is stored into a
rectangular external casing that is made of nickel-plated steel. As shown
in cross-sectional views of FIGS. 5A-5D, a sealing plate 160, spacer 20,
current collector 22, etc. are overlayed in listed order, then the layer
is penetrated by a shaft portion 181 of an electrode terminal element 18x
via a gasket 17 (FIGS. 5A-5D). Here, the shaft portion 181 penetrates
through the current collector 22 by passing through a pass-through 220
provided in the current collector 22, in such a manner that an apical
portion 187 projects out from the current collector, the apical portion
187 being provided in a first end of the shaft portion 181 in the
penetration direction. Once the shaft portion 181 penetrates through the
current collector 22, the apical portion 187 of the electrode terminal
element 18x, which has an opening 185, is expanded diametrically to form
a plate-like portion 182x by flaring the opening 185 with a jig inserted
thereinto.

[0008]Next, the plate-like portion 182x is pressed against the current
collector 22 in a plurality of steps (here, in two steps), such that a
main surface C' of the plate-like portion 182x comes into contact with a
main surface B of the current collector 22 (FIGS. 5C-5D). In a case where
the plate-like portion 182x has come into contact with the current
collector 22 only by getting pressed thereagainst, the electrical
resistance of the battery becomes unstable from the infiltration of
electrolyte or the like into between the plate-like portion 182x and the
current collector 22. For this reason, a laser beam is applied to a part
of the pressed area to weld the plate-like portion 182x to the current
collector 22, the laser beam being emitted from the proximity of the
plate-like portion 182x and perpendicular to its another surface E which
is exposed to an external space and is farther away from the current
collector 22 (FIG. 6A).

[0009]Then, the lead tab extending from the electrode assembly is
connected to the current collector 22. The sealing plate is fit into and
welded to the opening in the external casing. Electrolyte is inserted
inside the battery through a filler hole provided in the sealing plate.
Finally, the battery is sealed by plugging the filler hole with a sealing
plug.

[0010]However, there is a problem in the conventional manufacturing
process for a sealed battery: deficiencies in battery performance may
arise due to insufficient welding between an electrode terminal and a
current collector, as will be described below.

[0011]As shown in an area S1 of FIG. 6A, the plate-like portion 182x has a
slanted side 184x. The slanted side 184 makes an acute angle θ1
with the main surface B of the current collector 22. Here, in order to
properly perform laser-welding, it is necessary to partially melt the
plate-like portion 182x and the current collector 22 by applying a laser
beam to the proximity of a perimeter of an interface between the
plate-like portion 182x and the current collector 22.

[0012]Assume a case where a laser beam is applied in the area S1 so as to
weld the plate-like portion 182x to the current collector 22, the laser
beam being emitted from the proximity of the plate-like portion 182x and
perpendicular to its surface E. The problem here is that the slanted side
184, as well as a part of the main surface B that is surrounded by the
slanted side 184, is not exposed to the laser beam because a perimeter of
the surface E blocks the laser beam.

[0013]This may give rise to the following problems: (i) only the proximity
of the slanted side 184x melts from receiving thermal energy provided by
the laser beam, leaving the current collector 22 and the plate-like
portion 182x unmerged; and (ii) due to the interspace between the slanted
side 184x and the part of the main surface B that is surrounded by the
slanted side 184x, the perimeter of the surface E intensively receives
the thermal energy from the laser beam and eventually gets sputtered and
comes off from overheat, as shown in FIG. 6B.

[0014]Such problems caused by poor welding could not only damage the
stability of electrical conductivity between the electrode terminal and
the current collector, but also cause the sputtered, fallen portion to
enter inside the electrode assembly and trigger a short circuit. These
problems should thus be solved immediately so as to achieve a proper
battery performance.

SUMMARY OF THE INVENTION

[0015]The present invention is provided in view of the above problems. It
is an object of the present invention to provide a sealed battery that
can offer great battery performances and a manufacturing method therefor,
by unfailingly welding an electrode terminal and a current collector.

[0016]In order to solve the above problem, the present invention is a
sealed battery formed by hermetically sealing an external casing storing
therein an electrode assembly that is (i) electrically connected to a
current collector and (ii) formed by layering a positive electrode plate
and a negative electrode plate with a separator sandwiched therebetween,
the current collector being welded together with an electrode terminal,
wherein: the electrode terminal is composed of (i) a shaft portion, (ii)
a terminal portion provided in a first end of the shaft portion and (iii)
a frustum-shaped portion provided in a second end of the shaft portion;
the shaft portion penetrates through the current collector such that the
frustum-shaped portion projects out from the current collector; the
frustum-shaped portion has been pressed against the current collector
such that a bottom base of the frustum-shaped portion comes into contact
with the current collector; and the bottom base of the frustum-shaped
portion and the current collector have been welded together in at least
one area on a perimeter of the bottom base of the frustum-shaped portion.

[0017]In the sealed battery, the frustum-shaped portion may be an expanded
portion formed by diametrically expanding a shaft-like apical portion
that (i) is provided in the second end of the shaft portion and (ii) has
an opening that connects to an external space in the penetration
direction. Here, the shaft-like apical portion is diametrically expanded
by flaring the opening with a jig inserted thereinto.

[0018]In the sealed battery, the welding may be a laser beam spot-welding.

[0019]The frustum-shaped portion may have a shape of a conical frustum.

[0020]The present invention also provides a manufacturing method for a
sealed battery, comprising: a first step of (i) causing a terminal
element, which is composed of a shaft portion and an apical portion
provided in a first end of the shaft portion, to penetrate through a
current collector such that the apical portion projects out from the
current collector, (ii) shaping the apical portion into a plate-like
portion by expanding the apical portion diametrically and (iii) pressing
the plate-like portion against the current collector; a second step of
shaping the plate-like portion into a frustum-shaped portion whose bottom
base is facing the current collector; and a third step of welding the
bottom base of the frustum-shaped portion and the current collector
together in at least one area on a perimeter of the bottom base of the
frustum-shaped portion, such that the bottom base of the frustum-shaped
portion is in contact with the current collector.

[0021]In the second step of the manufacturing method, the plate-like
portion may be shaped into the frustum-shaped portion by deforming the
plate-like portion using a pressing die.

[0022]The present invention also provides a manufacturing method for a
sealed battery, comprising: a first step of causing a terminal element,
which is composed of a shaft portion and an apical portion provided in a
first end of the shaft portion, to penetrate through a current collector
such that the apical portion projects out from the current collector,
wherein the apical portion has a cup-shaped opening that connects to an
external space in the penetration direction; a second step of forming a
frustum-shaped portion whose bottom base is facing the current collector
by (i) diametrically expanding the apical portion by flaring the
cup-shaped opening with a jig inserted thereinto and (ii) pressing the
frustum-shaped portion against the current collector; and a third step of
welding the frustum-shaped portion and the current collector in at least
one area on a perimeter of the bottom base of the frustum-shaped portion.

[0023]According to the sealed battery of the present invention having the
above-described structure, the shaft portion of the electrode terminal,
which has penetrated through the current collector, has the
frustum-shaped portion (e.g., a conical frustum-shaped portion) whose
bottom base is adjacent to the main surface of the current collector, the
bottom base of the frustum-shaped portion having a larger surface area
than a top base thereof.

[0024]This structure allows making the entire bottom base of the
frustum-shaped portion come into contact closely with the main surface of
the current collector with no space therebetween. When viewing the top
base of the frustum-shaped portion perpendicular thereto, the perimeter
of the bottom base of the frustum-shaped portion, as well as the current
collector therearound, is exposed to the external space in the proximity
of the tapered slanted side of the frustum-shaped portion.

[0025]Accordingly, when welding the frustum-shaped portion to the current
collector by, for example, applying a laser beam perpendicular to the top
base of the conical frustum-shaped portion, the laser beam is applied
evenly and properly to the perimeter of the bottom base of the conical
frustum-shaped portion and the part of the current collector therearound.

[0026]As a result, both the conical frustum-shaped portion and the current
collector melt from receiving energy from the laser beam. Their molten
portions merge and solidify. This forms an even weld spot.

[0027]Unlike conventional technologies, the present invention can form an
excellent weld spot and thereby prevent the following problems: (i) only
the electrode terminal melts during the laser-welding, leaving the
electrode terminal and the current collector unmerged and resulting in
poor welding; and (ii) an internal short circuit occurs due to
sputtering/falling of a part of the conical frustum-shaped portion.

[0028]Therefore, with the above-described structure, the manufacturing
method for the sealed battery of the present invention can not only
alleviate an increase in the internal resistance triggered by poor
welding, but also offer stable battery performance even under an
undesirable condition, such as when electrolyte infiltrates into between
the electrode terminal and the current collector during use.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]These and the other objects, advantages and features of the
invention will become apparent from the following description thereof
taken in conjunction with the accompanying drawings which illustrate a
specific embodiment of the invention. In the drawings:

[0030]FIG. 1 shows a cross-sectional view showing a structure of a sealed
rectangular battery pertaining to a first embodiment of the present
invention;

[0031]FIGS. 2A-2C show the structure of the battery pertaining to the
first embodiment around a current collector and a positive electrode
terminal;

[0032]FIGS. 3A-3C show parts of a manufacturing process for the battery (a
manufacturing process for a sealing assembly) pertaining to the first
embodiment;

[0033]FIGS. 4A-4D show parts of a manufacturing process for a battery (a
manufacturing process for a sealing assembly) pertaining to a second
embodiment;

[0034]FIGS. 5A-5D show parts of a manufacturing process for a conventional
battery (a manufacturing process for a conventional sealing assembly);
and

[0035]FIGS. 6A-6B show the manufacturing process for the conventional
battery (the manufacturing process for the conventional sealing
assembly), as well as problems pertaining thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036]The following describes embodiments of the present invention.
However, the present invention is of course not limited to these
embodiments, and may be implemented in a variety of forms without
departing from the technical scope of the invention.

First Embodiment

1. Structure of Sealed Battery

[0037]FIG. 1 shows a perspective, cross-sectional view showing a structure
of a sealed battery, which is one embodiment of the present invention
(hereafter, simply "battery 1").

[0039]The external casing 15 has a rectangular external body with a closed
bottom, and formed by subjecting an aluminum alloy plate to a drawing
process. The rolled electrode assembly 14 and a predetermined amount of
electrolyte are stored into the external casing 15. The external casing
15 is sealed by laser-welding a rim 161 of a sealing plate 160 in the
sealing assembly 16 to an opening 151 of the external casing 15.

[0040]The sealing assembly 16 is composed of the sealing plate 160, which
is stamped out from an aluminum alloy plate, and a spacer 20, which is
provided below the sealing plate 160 facing a main surface of the sealing
plate 160. The sealing assembly 16 is constructed in such a manner that a
negative electrode terminal 18 penetrates through the center of the
sealing plate 160 and the spacer 20 via a gasket 17. A filler hole 21 is
formed in the sealing plate 160 for inserting electrolyte therethrough
into the external casing 15 in the manufacturing process. Once the
external casing 15 is filled with electrolyte, the filler hole 21 is
plugged.

[0041]The negative electrode terminal 18 is made of nickel. As shown in
FIG. 2A, the negative electrode terminal 18 is composed of: a disk-shaped
terminal portion 180 positioned outside the battery 1; a shaft portion
181 with an opening 185 that connects to the external space; and a
conical frustum-shaped portion 182 (a portion to be pressed) formed by
pressing an apical portion 187 that is provided in a first end of the
shaft portion 181. The first embodiment is different from conventional
battery structures in that the conical frustum-shaped portion 182 is
provided in the first end of the shaft portion 181 of the negative
electrode terminal 18, the shaft portion 181 penetrating through the
current collector 22 and partially protruding out from a main surface B
thereof by passing through a pass-through 220 provided along the
thickness direction of the current collector 22.

[0042]A bottom base C of the conical frustum-shaped portion 182 is pressed
against and thus in contact with the main surface B of the current
collector 22 in the proximity of the pass-through 220. Then, as shown in
FIG. 2B, the conical frustum-shaped portion 182 and the current collector
22 are laser-welded at a plurality of weld spots 183. FIG. 2B shows an
example where there are two weld spots 183. Here, the welding method of
this invention is not limited to the one described above. For example, it
is permissible to provide a substantial linear weld area within a
predetermined area such that each spot overlap with one another.

[0043]The spacer 20 is made by injection molding an insulation material
(e.g., polypropylene). Provided around the opening 151 of the external
casing 15, the spacer 20 holds the electrode assembly 14 against the
bottom of the external casing 15 and protects the electrode assembly 14
from vibration.

[0044]The current collector 22 is made of a metal plate with a high
electrical conductivity. The bottom base C of the conical frustum-shaped
portion 182 has been pressed against and thus in contact with the main
surface B of the current collector 22 in the proximity of the
pass-through 220. Later the conical frustum-shaped portion 182 and the
current collector 22 are laser-welded. The current collector 22 is
connected by resistance welding via a lead tab 19 to a negative electrode
plate 12 of the electrode assembly 14, the lead tab being made of a
nickel-plated conductor material.

[0045]The electrode assembly 14 is formed by rolling a positive electrode
plate 11, a separator 13, a negative electrode plate 12, and another
separator 13 that are layered over one another in listed order (these are
all belt-like). The rolled layer is then placed on its side and flattened
to give the rolled layer a flat cross-section.

[0046]In order to secure energy density, it is desirable that a capacity
of the electrode assembly 14 is set as large as possible in accordance
with a volume of the external casing 15.

[0047]The positive electrode plate 11 is formed by applying a positive
electrode mixture composed of a conductive agent and a binding agent onto
a surface of a positive electrode core (e.g., aluminum), wherein a major
constituent of the positive electrode mixture is a lithium cobalt
composite oxide (e.g., LiCoO2) which is the active material for the
positive electrode. The positive electrode plate 11 is electrically
connected via a conductive tab (not illustrated) to an inner wall of the
external casing 15. This makes the bottom of the external casing 15
function as the positive electrode terminal.

[0048]The negative electrode plate 12 is formed by applying a negative
electrode mixture composed of a conductive agent and a binding agent onto
a surface of a negative electrode core (e.g., copper), wherein a major
constituent of the negative electrode mixture is a carbonaceous material
which is the active material for the negative electrode.

[0049]Each separator 13 is a microporous film made of polyethylene and is
used to insulate the positive electrode plate 11 from the negative
electrode plate 12. Each separator 13 has a temperature limit of up to
approximately 120° C.

[0050]In FIG. 1, for simplicity, each separator 13 has a rectangular shape
and its size is about the same as the positive and negative electrode
plates 11 and 12. However, it is permissible that one of these separators
13 is formed in the shape of an envelope, so that the positive electrode
plate 11 can be inserted into the envelope-like separator 13 to insulate
itself from the negative electrode plate 12.

[0051]The electrolyte, which is impregnated into the electrode assembly
14, has a nonaqueous composition, such as 1MLiPF6-EC/DMC (ratio by
volume is EC:DMC=30:70 at 25 degrees C.).

[0052]The lithium-ion battery 1 with the above-described structure
produces the following phenomena while being charged. In the positive
electrode plate 11, lithium included in lithium cobalt oxide develops
into an ion (Li→Li++e.sup.-), and a lithium ion (Li+)
moves through the separators 13 to the negative electrode plate 12.

[0053]Meanwhile, in the negative electrode plate 12, the lithium ion
Li+ is incorporated into layers of a carbon crystal that constitutes
graphite.

[0054]When in a discharge state, the lithium-ion battery 1 exhibits a
battery reaction that is opposite to the above, externally providing
power (e.g., 800 m Ah).

[0055]The characteristic of the battery 1 lies in its structure around the
weld spots connecting the conical frustum-shaped portion 182 of the
negative electrode terminal 18 and the current collector 22. That is, as
shown in FIG. 4D, the conical frustum-shaped portion 182 of the negative
electrode terminal 18 has its entire bottom base C in contact with the
main surface B of the current collector 22 and its top base D located
away from the current collector 22 (the bottom base C has a larger
surface area than the top base D).

[0056]With this structure, the diameter of the conical frustum-shaped
portion 182 is smaller toward its top base D. That is, the conical
frustum-shaped portion 182 is tapered to make a slanted side 184. The
slanted side 184 and the main surface B form an obtuse angle θ2. It
should be noted that, specifically, the angle θ2 is desirably in
the range of 120 degrees to 150 degrees, inclusive.

[0057]This conical frustum-shaped portion 182 offers the following
advantage. In the manufacturing process, in a case where a laser beam is
emitted either perpendicular to the top base D (opposite of the z
direction) or nearly perpendicular to the top base D (e.g., at an angle
approximately 10 degrees off the right angle), the laser beam is applied
to an area on both the current collector 22 and a perimeter of the bottom
base C of the conical frustum-shaped portion 182. This way the current
collector 22 and the conical frustum-shaped portion 182 are melted in the
stated area; the molten portions then merge and become solid to fix each
other. This makes possible excellent spot welding.

[0058]The following are descriptions of the aforementioned characteristic
and a manufacturing process of the sealing assembly 16.

2. Manufacturing Process of Sealing Assembly 16

[0059]As will be described below, in the manufacturing process pertaining
to the first embodiment, the following steps are taken in listed order:
(i) a forming step to form the conical frustum-shaped portion 182 and
(ii) a welding step to weld the conical frustum-shaped portion 182 to the
current collector 22.

[0060]First, an electrode terminal element 18x (the negative electrode
terminal 18, yet to be pressed) is provided (aforementioned FIG. 5A).
Then the shaft portion of the electrode terminal element 18x is arranged
in such a manner that it penetrates via the insulative gasket 17 through
the sealing plate 160, the spacer 20 and the pass-through 220 of the
current collector 22 in listed order (FIG. 5B).

[0061]Second, with use of a certain type of pressing die, the apical
portion 187 around the opening 185 is pressed and expanded
diametrically--i.e., in the direction orthogonal to the axis of the shaft
portion 181 (here, in the horizontal direction)--by flaring the opening
185 with a jig inserted thereinto. This is called a diametrically
expanding step. (Note, the apical portion 187 is provided in the first
end of the shaft portion 181 that has penetrated through the current
collector 22. The opening 185 has been provided in the apical portion 187
parallel thereto and connects to the external space.) This pressing
process is performed in a plurality of steps (two steps shown in FIGS. 5C
and 5D), with the result that the apical portion 187 is expanded
diametrically. This forms the plate-like portion 182x (FIG. 5D).

[0062]Next, a pressing die A shown in FIG. 3A is provided. Here, a surface
B' of the processing punch A has a depression that is complementary to
the plate-like portion 182x having a shape of a conical frustum. The
depression has a slanted side A1 that makes a predetermined angle with a
depressed surface of the pressing die A (e.g., a line parallel to the
main surface B and the slanted side A1 form an angle of 2π-θ2).
Then, the pressing die A is pressed against the plate-like portion 18x in
such a manner that the slanted side A1 is directly in contact with the
perimeter of the plate-like portion 182x. This is the forming step of
partially deforming the plate-like portion 182x (FIG. 3A). As a result,
the plate-like portion 182x turns into the conical frustum-shaped portion
182 (FIG. 3B). Upon formation of the conical frustum-shaped portion 182,
its slanted side 184 makes an obtuse angle θ2 with the main surface
B that is exposed to the external space around the slanted side 184 (FIG.
3B).

[0063]Next, the welding step is performed, in which the laser beam is
applied either perpendicular or nearly perpendicular to the top base D of
the conical frustum-shaped portion 182. FIG. 3C is an enlarged view of an
area S2 shown in FIG. 3B. The laser beam is applied to an area on, at
least, the slanted side 184 and the main surface B which is exposed to
the external space around the slanted side 184.

[0064]Here, in the area S2, the entire bottom base C of the conical
frustum-shaped portion 182 is properly bonded with the main surface B of
the current collector 22. The slanted side 184, as well as the part of
the main surface B surrounding the slanted side 184, is exposed to the
laser beam emitted perpendicular to the main surface B. Hence, energy of
the laser beam evenly reaches both the current collector 22 and the
slanted side 184 that then melt, merge and solidify. This forms a weld
spot (a weld nugget) in an area subjected to the laser-welding. The
aforementioned process makes the sealing assembly 16.

[0065]As has been described above, in the first embodiment, the slanted
side 184, as well as the part of the main surface B surrounding the
slanted side 184, is exposed to the laser beam emitted in the welding
step. As opposed to conventional technologies, the plate-like portion
182x of the present embodiment does not shield the current collector 22
from the laser beam. It is thus possible to prevent several problems,
such as poor welding, sputtering/falling of a part of a component, etc.,
and to properly weld the conical frustum-shaped portion 182 to the
current collector 22.

[0066]It should be noted that, depending on the method of pressing the
apical portion 187 against the current collector 22, there may be a case
where the entire bottom base C of the conical frustum-shaped portion 182
is not in contact with the main surface B, but only a part (e.g., the
perimeter) of the bottom base B is in contact with the main surface B.
However, even in such a case, the laser beam is applied in the welding
step to the area S2 where the current collector 22 and the conical
frustum-shaped portion 182 are bonded with each other. This forms an
excellent weld spot 183.

[0067]The "conical frustum-shaped portion" of the present invention does
not have to be in a mathematically defined shape. It is permissible that
the conical frustum-shaped portion is roughly in a shape of a conical
frustum. A somewhat deformed conical frustum-shaped portion is
acceptable. More specifically, the conical frustum-shaped portion may
have any substantial shape formed by the pressing process etc. For
example, the conical frustum-shaped portion may have a depression in the
center of its top base D.

[0068]Furthermore, the top base D of the conical frustum-shaped portion
182 does not need to have a perfectly flat surface, but may have a bulgy
surface extending from the slanted side 184. More specifically, it is
permissible to form the conical frustum-shaped portion 182 in an
approximately hemispherical shape, a gentle globular shape, etc.

[0069]The bottom base C does not need to have a shape of a circle, either.
The perimeter of the bottom base C may include a curved line, or may be
polygonal.

Second Embodiment

[0070]The following describes the second embodiment, with a focus on
differences between the first and second embodiments.

[0071]In the first embodiment, the conical frustum-shaped portion 182 is
formed in the forming step by first pressing the apical portion 187
against the current collector 22 and then deforming the plate-like
portion 182x using the pressing die A. This manufacturing method,
however, is not a limitation of the present invention.

[0072]FIGS. 4A-4D show a manufacturing method pertaining to the second
embodiment. As shown in the method in these FIGs., it is permissible to
use an electrode terminal element 18a that has the following structure.
The electrode terminal element 18a has a shaft portion 181 and an apical
portion 188 provided in a first end of the shaft portion 181. In the axis
direction of the shaft portion, the apical portion has a cup-like opening
185 that connects to the external space and has a slanted side 186.

[0073]The electrode terminal element 18a having the above-described
structure makes possible the following manufacturing method. The sealing
plate 160, the spacer 20 and the pass-through 220 of the current
collector 22 are penetrated by the apical portion 188 and the shaft
portion 181 (an insertion step, FIGS. 4A-4B). Next, the first pressing
step is performed--i.e., the apical portion 188 is diametrically expanded
halfway by flaring the opening 185 with a jig inserted thereinto. Then,
the second pressing step is performed--i.e., the apical portion 188 is
further expanded diametrically by further flaring the opening with
another jig inserted thereinto (FIG. 4C), so as to form the conical
frustum-shaped portion 182 (a diametrically expanding step, FIG. 4D). In
the example shown in these FIGs., an outer surface of the apical portion
188 becomes the bottom base C of the conical frustum-shaped portion 182,
and the slanted side 186 of the opening 185 in the apical portion 188
becomes the slanted side 184 of the conical frustum-shaped portion 182,
eventually.

[0074]Then the bottom base C of the conical frustum-shaped portion 182 is
pressed against the main surface B. Finally the welding step is
performed, just like in the first embodiment.

[0075]According to the aforementioned method, the slanted side 186 makes
an obtuse angle with the main surface B just like the slanted side 184
pertaining to the first embodiment, without using the pressing die A
after the pressing process. Also, the entire bottom base C is in contact
with the main surface B, just like in the first embodiment. Therefore,
the second embodiment 2, which incorporates the above-described electrode
terminal element 18a, can not only achieve the same effect as the first
embodiment in the welding step of welding the conical frustum-shaped
portion 182 to the current collector 22, but also further simplify the
manufacturing process.

Manufacturing Embodiment Examples

[0076]Inventors of the present invention have manufactured the battery of
the first embodiment as an embodiment example, and evaluated its battery
performance through various experiments.

(Quality Evaluation of Laser-Welding)

[0077]The inventors manufactured (i) embodiment examples, each of which is
the battery 1 having the conical frustum-shaped portion 182 and (ii)
comparative examples, each of which is the same as the embodiment example
except that it has the plate-like portion 182x. In each of the embodiment
and comparative examples, the inventors laser-welded a negative electrode
terminal to a current collector. Later they visually examined for poor
welding at weld spots. The laser beam was set at pulse width 1.6 ms,
pitch 0.22, output 1.0 J/p, and beam angle 10 degrees.

[0078]Results of this experiment are shown in Table 1.

TABLE-US-00001
TABLE 1
Results of Qualify Evaluation of Laser-Welding
Embodiment Examples Comparative Examples
Poor Welding confirmed in 0 out of confirmed in 74 out of 500
500 batteries batteries
Breakdown of n/a sputtering: confirmed in 11
Defects out of 500 batteries;
poor welding (only the
terminal was melted):
confirmed in 63 out of 500
batteries
* Manufactured batteries, both embodiment and comparative examples, each
had a size of 4.2 × 33.7 × 42.5 (mm).
* The laser beam was set at pulse width 1.6 ms, pitch 0.22, output 1.0
J/p, and beam angle 10 degrees. The taper angle of the slanted side of
the conical frustum-shaped portion was set at 30-60 degrees.

[0079]As indicated by the results of the experiment shown in Table 1, the
inventors confirmed that in some of the comparative examples, only the
perimeter of the slanted side 184x of the plate-like portion 182x was
melted, with the result that the plate-like portion 182x failed to
partially melt and merge with the current collector 22--i.e., the
plate-like portion 182x was merely in contact with the current collector
22 (these batteries are referred to as poorly welded batteries). The
inventors also confirmed that, in some of the comparative examples, a
part of the plate-like portion 182x was lost due to sputtering (these
batteries are referred to as sputtered batteries), although fewer in
number than the poorly welded batteries.

[0080]In contrast to the comparative examples, the embodiment examples
obtained significant improvements in welding. Out of 500 embodiment
examples, none had the problem of poor welding. In this view, it is
confirmed that the weld spots in the embodiment examples are securely
formed owing to use of the conical frustum-shaped portion 182.

(Evaluation of Battery Reliability)

[0081]Predetermined drop test, heat shock test, and high-temperature and
high-humidity test were performed on both the embodiment and comparative
examples that had been subjected to the aforementioned laser-welding. The
inventors then evaluated battery reliability after each test, based on
the increase in the internal resistance value of each battery. The number
of embodiment examples and comparative examples on which these tests were
performed was N=10 each.

[0083]As a result of the drop test, it is confirmed that the sputtered
batteries and the poorly welded batteries of the comparative examples
both experienced a significant increase in the internal resistance value.
One possible reason for such an increase in the internal resistance value
is that, because the negative electrode terminal 18x and the current
collector 22 in each comparative example are not welded at weld spots in
an intended manner, the electrolyte infiltrates into the weld spots due
to the shock/vibration of the drop, rendering the electrical conductivity
between the negative electrode terminal 18x and the current collector 22
unstable. Furthermore, the inventors confirmed that the negative
electrode terminal 18x came off the current collector 22 in 3 out of 10
poorly welded batteries, because a mechanical load was consecutively
applied to the inside of the batteries. In these 3 poorly welded
batteries, the electrical conductivity between the negative electrode
terminal 18x and the current collector 22 was unstable, just like in the
sputtered batteries described earlier.

[0084]On the other hand, in the embodiment examples, the negative
electrode terminal 18 is securely welded to the current collector 22 due
to use of the conical frustum-shaped portion 182. It is therefore
considered that each embodiment example retains an excellent electrical
conductivity and alleviates the increase in the internal resistance
value, even when the shock/vibration of the drop has caused the stated
infiltration of electrolyte.

[0085]This stability of the electrical conductivity was mostly confirmed
in the embodiment examples subjected to the heat shock test and the
high-temperature and high-humidity test as well. That is to say, although
the internal resistance value increased in both of the embodiment and
comparative examples after performing each test, there was less variation
in the increase of the internal resistance value between the embodiment
examples, and the extent of the increase was small in the embodiment
examples. In this view, it can be said that the embodiment examples are
evidently superior to the comparative examples.

[0086]The superiority of the present invention has been confirmed from
performing the above experiments on the embodiment examples.

<Additional Remarks>

[0087]The above embodiments have described an example in which the present
invention is applied (but not limited) to a lithium-ion battery. The
present invention may also be applied to a nickel-metal hydride battery
and various other types of batteries.

[0088]Further, the first embodiment has exemplarily depicted the electrode
assembly 14 formed by rolling the belt-like negative and positive
electrode plates 11 and 12 that have been layered with the separator 13
sandwiched therebetween. However, it is permissible to use an electrode
assembly formed by layering rectangular-shaped (stacked) electrodes and
separators.

[0089]Each embodiment has exemplarily described the structure of the
conical frustum-shaped portion 182 in the electrode terminal 18 and a
manufacturing method therefor. However, if the shaft portion 181 of the
electrode terminal 18 has a rectangular or polyhedral shape, implementing
the manufacturing method described in each embodiment may lead to the
formation of a rectangular or polygonal frustum-shaped portion. Hence, in
the present invention, the frustum-shaped portion formed in the first end
of the shaft portion is not limited to a conical frustum-shaped portion,
but may be such a rectangular or polygonal frustum-shaped portion.

[0090]The present invention aims to solve the problem of poor welding
between the current collector 22 and the electrode terminal 18 by forming
the plate-like portion 182x of the electrode terminal element 18x into
the conical frustum-shaped portion 182 or the like. Accordingly, the
plate-like portion 182x may be formed in such a manner that the
plate-like portion 182x is tapered to make a slanted side 184 (as in FIG.
2) only partially--i.e., only in the area to be welded. With this
structure, the same effect as that derived from each embodiment can be
expected.

[0091]Also, the weld spots 183 have been exemplarily described to be
formed by laser-welding. This, however, is not a limitation of the
present invention. The welding posts 183 may be formed by using other
energy beams. Further, a shape of each weld spot is not limited to
something recognizable from its outer appearance. Alternatively it is
permissible to form, for example, a weld spot 183 composed of multiple
weld spots that, as a whole, form a line by being adjacent to one
another.

[0092]It should be noted that the sealed battery and the manufacturing
method therefor pertaining to the present invention can be used, for
example, in a manufacturing method for a rectangular lithium-ion battery
for use as a general power source.

[0093]Although the present invention has been fully described by way of
examples with reference to the accompanying drawings, it is to be noted
that various changes and modifications will be apparent to those skilled
in the art. Therefore, unless otherwise such changes and modifications
depart from the scope of the present invention, they should be construed
as being included therein.